Lock-chamber devices are generally required in installations for separating dust from gases which are under a high pressure than the space into which the dust is to be discharged. Installations of this type include electrostatic separators, cyclones and other systems having bins maintained at an elevated pressure from which the dust is to be discharged into a collector at atmospheric pressure.
If such systems are provided with flap-type outlets which are intermittently opened to the low-pressure space, gas at high velocity tends to escape and will entrain and agitate the dust in an undesirable manner.
An escape of gas itself is undesirable because it constitutes an unavoidable loss of the gas or is ecologically intolerable, especially when the low-pressure space is the atmosphere. For this reason the the dust must be discharged from such pressurized systems through lock chambers.
So-called "starwheel" lock chamber devices are known and comprise a starwheel disposed in a cylindrical housing which, together with the wall of the housing, defines a plurality of revolving cells which can be filled with dust through an inlet connected to the housing and from which the dust can be discharged through an outlet.
The number and arrangement of the blades of the starwheel are so selected as to preclude any direct communication from the inlet to the outlet. In other words, any cell communicating with the inlet does not simultaneously communicate with the outlet but only opens into the latter after it has been removed from alignment with the inlet.
Such starwheel lock chambers require a good seal between the rotating starwheel and the housing wall if effective removal of dust without discharge of gas or reduction of the pressure at the inlet is to be obtained.
Because the dust often contains hard components, which subject all materials to strong abrasion, the sealing surfaces of the starwheel lock chamber are subjected to heavy wear. In addition the starwheel must be virtually sealed throughout the periphery of the lock chamber so that the provision of resilient means to maintain a pressure contact between the sealing surfaces and compensate for wear, even to a limited extent, involves high structural expense.
As an alternative to starwheel lock chambers, so-called "swinging gate" lock chambers have been proposed, the latter enabling the filling of a separate lock chamber with dust and a discharge of the dust from the lock chamber in an intermittent operation. Where the pressure differentials across the system are high, the dust-discharge opening of such devices must be relatively small because the means for actuating the gate would otherwise have to be of high capacity. Furthermore, openings of a certain size are required if dust is to be collected at a given rate. These mutually contradictory requirements preclude the devices which have been proposed from being used in all conceivable applications requiring maintenance of pressure at the inlet to the lock chamber.